Open pit mining and exploration drilling in a gold deposit in Central Brazil, about 400 km NW of Brasilia, has provided exposure of regolith materials for detailed observation and sampling. The area is dominated by a seasonally humid climate with annual precipitation of 1500 mm and "Cerrado" vegetation. The region has experienced a history of lateritic weathering and resulted in a landscape with plateau surfaces where lateritic profiles are generally preserved and gently undulating surfaces which may present stone line horizons down to two metres below the surface. Lateritization is thought to have developed during the aggradation phases of the Velhas geomorphological cycle in Lower Plesitocene (Braun, 1970). Incision of these surfaces has led to the degradation of the lateritic crust and formation of stone lines (Lecomte, 1988).

The weathering profile over the deposit shows a stone line horizon which is rich in quartz fragments and contains remnants of lateritic materials. Mass balance calculations, based on the geochemical immobility of Ti and Zr show absolute accumulation of Au, Fe and Si, indicating that quartz, lateritic materials and Au were added to the profile. Gold distribution in saprolite, stone line horizon and the top soil are very similar, showing that Au accumulation took place essentially downwards by chemical and mechanical processes (Porto & Hale, 1995). Lateritic materials have been mechanically worn but show geochemical signatures of the mineralized zone, indicating that they have accumulated in the stone line mechanically over the deposit area. Quartz fragments probably accumulated in a similar fashion but fragments directly derived from vein strutures in the saprolite are also present.

The stone line is of a local origin and has formed by progressive downwards accumulation of materials into the residual soil and were only locally displaced laterally during the lowering of the land surface.